As it is known in the art, transformers are typically used for providing current and voltage conversion. A transformer may be used to decrease or "step-down" a voltage or alternatively the transformer may be used to increase, or "step-up" a voltage. One use for transformers is in computer power supply design to step down voltages to levels that may be used by components on an integrated circuit board.
Standard transformers that have been used in integrated circuit design have included a magnetic core, a primary winding, a secondary winding and a bobbin. During manufacture, both windings are wound around the bobbin and then placed in the magnetic core. Once the winding and bobbin combination are placed in the core, the leads of the winding may be passed through the bobbin to terminators on the board. Thus, the bobbin serves a dual purpose; to support the windings and also to provide a pathway for wires out of the transformer to the termination on the circuit board.
However, one problem with the standard transformer design is that it has a relatively large profile with respect to the other components on the circuit board. As technological advances have provided more compact and complex integrated circuitry, there is a need to provide computer products having increased performance in a decreased size. Thus, there is a need to pack circuitry more closely together.
It is therefore desirable to maximize the use of space in a transformer having a very small profile. To obtain maximum performance for the transformer, a goal is to fit as much copper into the interior space of the transformer as possible. This is because the more copper that is provided in the transformer, the thicker the conductor and the lower the associated losses. A window utilization factor provides a measurement of the amount of the transformer that is used to pack copper and consequently gives an indication as to the performance capabilities of the transformer. The window utilization factor is a ratio of the area of copper within the transformer to the window space of the transformer. Ideally, a ratio of 1, indicating that the window is 100% utilized with copper would be desirable.
However, because the standard transformer includes a bobbin, the window utilization factor of the standard transformer is less than 1. In fact, because the bobbins of the transformers are subject to minimum thickness requirements, as the profile of the transformer is reduced, the bobbin utilizes a greater percentage of the window area. As a result, the window utilization factor is further reduced. Thus, it is difficult to provide a high performance low profile standard transformer because the amount of copper that is capable of being placed in the transformer is limited by the amount of space required by the bobbin.
One transformer design that provides high power with a low profile is an integrated magnetics transformer. In integrated magnetics transformers, one or more winding are etched into a multi-layered circuit board while the core enclosing the board may or may not include the other windings. Transformer terminations are provided via through holes on the integrated circuit board. Although the integrated magnetic transformers may be used to provide low profile power conversion, it is often difficult to obtain the desired amount of copper cross-section on the circuit board, therefore making it difficult to obtain the desired power conversion capabilities. In addition, to decrease the size of the circuit board, increasingly complex and expensive technologies must be used, making this solution to the problem of providing a low profile transformer undesirable.